jscd 0.3.0

Reverse bytenode-compiled .jsc (V8 code cache) back to JavaScript
Documentation 
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// 语料生成器：与 bytenode 完全同参地编译 JS → .jsc。
// bytenode 的关键动作：--no-lazy + --no-flush-bytecode（全部函数即时编译、字节码不被 GC 丢弃），
// 然后 vm.Script(code, {produceCachedData}) / script.createCachedData()。
// 用法: node mkcorpus.js <input.js> <output.jsc> [--brotli] [--module]
const fs = require('fs');
const vm = require('vm');
const v8 = require('v8');

const [input, output, ...flags] = process.argv.slice(2);
if (!input || !output) {
  console.error('usage: node mkcorpus.js <input.js> <output.jsc> [--brotli] [--module]');
  process.exit(2);
}

v8.setFlagsFromString('--no-lazy');
if (Number(process.versions.node.split('.')[0]) >= 12) {
  v8.setFlagsFromString('--no-flush-bytecode');
}

let code = fs.readFileSync(input, 'utf8');
// 与 bytenode compileFile 一致：剥离 shebang
if (code.startsWith('#')) {
  const nl = code.indexOf('\n');
  code = nl === -1 ? '' : code.slice(nl + 1);
}
// 真 ESM（import/export/顶层 await）必须走 SourceTextModule 才能出 code cache；
// bytenode 对 .mjs 也是这么做的。CJS 式 --module 只是包一层 wrapper。
const looksEsm = /^\s*(?:import|export)\b/m.test(code) || /(^|\n)\s*await\s+/.test(code);
const asModule = flags.includes('--module') || looksEsm;
if (asModule && typeof vm.SourceTextModule === 'function') {
  const mod = new vm.SourceTextModule(code, { produceCachedData: true });
  let cache = mod.cachedData;
  if (!cache || cache.length === 0) {
    cache = mod.createCachedData();
  }
  let outM = Buffer.from(cache);
  if (flags.includes('--brotli')) {
    outM = require('zlib').brotliCompressSync(outM);
  }
  fs.writeFileSync(output, outM);
  process.exit(0);
}
if (asModule) {
  code = require('module').wrap(code);
}

const script = new vm.Script(code, { produceCachedData: true });
let cache = script.cachedData;
if (!cache || cache.length === 0) {
  cache = script.createCachedData();
}
let out = Buffer.from(cache);
if (flags.includes('--brotli')) {
  out = require('zlib').brotliCompressSync(out);
}
fs.writeFileSync(output, out);
console.log(`${process.versions.node} v8=${process.versions.v8} -> ${output} (${out.length} bytes)`);